Small Jellyfish as a Supplementary Autumnal Food Source for Juvenile Chaetognaths in Sanya Bay, China

Abstract

Information on the in situ diet of juvenile chaetognaths is critical for understanding the population recruitment of chaetognaths and their functional roles in marine food web. In this study, a molecular method based on PCR amplification targeted on 18S rDNA was applied to investigate the diet composition of juvenile Flaccisagitta enflata collected in summer and autumn in Sanya Bay, China. Diverse diet species were detected in the gut contents of juvenile F. enflata, including copepods, small jellyfish, anthozoa, polychaetes, echinoderms, diatoms and dinoflagellates. The diet composition showed obvious differences between summer and autumn. Copepod, such as Temora turbinata, Canthocalanus pauper and Subeucalanus crassus, dominated the diet in summer, representing up to 61% of the total prey items. However, small jellyfish, mainly consisting of Bougainvillia fulva, Solmissus marshalli and Pleurobrachia globosa, was the main food group (72.9%) in autumn. Environmental parameters showed no significant difference between summer and autumn. The mean abundance of juvenile chaetognaths in autumn was about eight times higher than that in summer, while the abundance of potential food prey was similar in both seasons. Our results suggested that juveniles chaetognaths might consume small jellyfish as a supplementary food source under enhanced feeding competition in autumn.